The invention relates, in general, to a measuring system for recognition of surface features of a product, e.g. flat glass, rapidly moved on a conveyor and having a surface which at least partially reflects and/or scatters light, and in particular to a measuring system of a type including a sensor system comprised of a plurality of transmitter/detector elements, preferably of infrared-LED and photodiodes and phototransistors, and directed towards the reflecting and/or scattering surface and stationery relative to the moving product, wherein the light radiating from a transmitter and reflected and/or scattered is received by the associated detector or by the neighboring detectors and converted into an electric signal, and wherein the plurality of transmitter/detector elements is arranged along at least one line extending transversely to the conveying direction of the product and vertically offset to the conveyor.
Many industrial processes which carry out the treatment of rapidly moving product aspire a differentiation between the individually moved pieces which oftentimes area arranged side-by-side on the conveyor.
This is achieved heretofore by several different solutions. It was possible through determination of the dimensions of the product to realize a satisfactory identification. CCD line cameras utilized for this purpose can, however, receive only a limited solid angle. In addition, optical distortions which adversely affect the accuracy of measurement are encountered. In conjunction with flat glass plates, this process has proven inappropriate as the dimensions, such as length and width, cannot be determined with sufficient measuring accuracy. Optical light barriers for dimensional determination have again the significant drawback that different surface conditions of the flat glass yield varying results as a consequence of scattered light.
A further proposal to enable an identification of rapidly moving product views the surface condition as differentiating feature as the product can be easily differentiated thereby.
Especially many applications and fields of operation exist in the glass producing industry because frequently a determination of the surface features must be undertaken, without encountering a shutdown of the manufacturing process.
German Pat. No. DE-A1-28 47 935 discloses an apparatus for automatically detecting defects, contamination or the like of transparent materials such as flat glass, including an optical transmitter arranged transversely to the transport direction of the specimen, and a respective receiver which is movable in transverse direction at parallel distance to the specimen and occupying thereby either a transmission position or a reflection position with respect to the transmitter. The optical receiver is composed of a row of measuring cells and moves during advance of the specimen, with the number of measuring cells depending on the rate of feed. A scanning of the surface is executed to determine even slightest imperfections or contamination.
The optical transmitter is provided in the form of a constant radiation source which is uniformly effective across the entire width of a flat glass pane and examines by light the flat glass pane passing by. Located on the other side is the optical receiver which is composed of several measuring cells and movable at very high speed transversely to the transport direction of the flat glass pane. If an imperfection is encountered during the movement of the receiver, a different measuring value is received. This deviation is converted into an electrical signal to thereby illuminate a signal lamp.
In particular for identification of flat glass plates cut to size according to customer specifications, in addition to other parameters the recognition of surface features is required which the flat glass plates exhibit after the various manufacturing processes.
If the flat glass plates should be subjected, for example, to a tempering process, the flat glass plates must be guided through the tempering oven after being cut to size and possibly treated with a surface coating. As a consequence of the high process temperature, the glass plates cannot be labeled. As the capacity of the tempering oven should be exploited to a highest possible degree, several plates of different shape are typically transported simultaneously through the tempering oven.
After exiting the oven, the plates can be identified with respect to their surface features and associated to respective order data. As the outer shape of the plates of a toughened batch oftentimes differs only slightly, the probability of error during an identification through determination of the dimensions after discharge is relatively high. Therefore, attempts were made to detect a further differentiating criterion in addition to the surface features.
Considered as surface features can be coatings, surface textures, markings, e.g. bar codes etc. In view of the high velocities by which the product is sometimes moved, recognition of surface features can be done by conventional means only in a very difficult manner. In addition, it may be necessary to recognize surface imperfections, e.g. chips, which occur primarily in the area of the edges.
In this context, U.S. Pat. No. 3,835,332 discloses an apparatus for detection of production errors in a web, e.g. a film track. A bar arranged transversely to the direction of movement of an endless film track is equipped with light-emitting diodes in side-by-side disposition for radiating pulsing light which is received by opposing photosensors and converted into a digital code which represents the intensity of the detected light. The detector can thereby be arranged either in transmission position or in reflection position. In this manner, a photographic film can be examined for defects or inaccuracies of the film thickness. The light-emitting diodes are illuminated in sequentially continuously repeating sequence for short intervals, and the reflected light or light transmitted through the track is detected and stored. The recorded data are compared with reference values obtained during a calibration mode of operation in order to detect defects in the web or in the web coating.
The sequential, pulsing control of the light-emitting diodes results in a scanning across the bar arranged transversely to the direction of movement, with the sensors associated to the light-emitting diodes receiving the reflected light pulses or light pulses transmitted through the web for conversion into electric signals. These signals are associated sequentially by an analog-digital-converter in dependence on the intensity to a code which is further processed digitally.